1. Field of the Invention
The present invention relates a cylindrical secondary battery, and more particularly, to a secondary battery capable of ensuring maximum battery stability without degrading battery performance.
2. Description of the Related Art
The rapid development of compact and lightweight portable electronic devices in recent times has created a growing need for compact and high-capacity batteries. In particular, use of lithium secondary batteries is rapidly increasing because they have a high energy density per unit weight and an operating voltage of 3.6 V or higher, which is 3 times higher than nickel-cadmium or nickel-metal hydride batteries that are widely used in portable electronic devices.
Lithium secondary batteries produce electric energy by redox reactions occurring when lithium ions are intercalated or deintercalated at positive and negative electrodes. Lithium secondary batteries use a material capable of reversibly intercalating or deintercalating lithium ions as active materials for positive and negative electrodes, and have an organic or polymer electrolyte between the positive electrode and the negative electrode.
Lithium secondary batteries include an electrode assembly wound in a jelly-roll shape, in which a separator is interposed between a negative electrode and a positive electrode. These batteries also include a can housing the electrode assembly and an electrolyte, and a cap assembly disposed over the can.
Lithium secondary batteries have the potential to explode or catch fire when subjected to overcharging or overcurrent, and thus they require a safety device to prevent overcharging of the batteries.
Generally, since lithium secondary batteries are fabricated by adding gasification materials such as biphenyl (BP) or cyclohexylbenzene (CHB) to the electrolyte, a large amount of gas is generated during overcharging of the battery, thus operating a current interrupting means. However, it is difficult to exactly control the amount of gas, and when too much gas is added, the lifespan of the battery may decrease and various side reactions may occur.
Meanwhile, as the cost of lithium cobalt dioxide (LiCoO2) used as the positive electrode active material increases, a relatively low-cost, nickel-based positive electrode active material such as NCM or NCA is being looked to as an alternative.
However, the nickel-based positive electrode active material such as NCM or NCA does not generate a sufficient amount of gas during overcharging of the battery.
That is, when the battery is overcharged, generation of a certain amount of gas in the battery operates the current interrupting means to interrupt current and ensures stability of the battery. However, since the nickel-based positive electrode active material does not generate a sufficient amount of gas in the case of a conventional battery design, the current interrupting means may not operate soon enough to ensure battery stability.